aliases.py

# -*- coding: utf-8 -*-
"""Aliases for the xonsh shell."""
import os
import re
import sys
import inspect
import argparse
import builtins
import collections.abc as cabc

from xonsh.lazyasd import lazyobject
from xonsh.dirstack import cd, pushd, popd, dirs, _get_cwd
from xonsh.environ import locate_binary, make_args_env
from xonsh.foreign_shells import foreign_shell_data
from xonsh.jobs import jobs, fg, bg, clean_jobs
from xonsh.platform import (
    ON_ANACONDA,
    ON_DARWIN,
    ON_WINDOWS,
    ON_FREEBSD,
    ON_NETBSD,
    ON_DRAGONFLY,
)
from xonsh.tools import (
    XonshError,
    argvquote,
    escape_windows_cmd_string,
    to_bool,
    swap_values,
    strip_simple_quotes,
    ALIAS_KWARG_NAMES,
    unthreadable,
    print_color,
)
from xonsh.replay import replay_main
from xonsh.timings import timeit_alias
from xonsh.xontribs import xontribs_main
from xonsh.ast import isexpression

import xonsh.completers._aliases as xca
import xonsh.history.main as xhm
import xonsh.xoreutils.which as xxw


@lazyobject
def SUB_EXEC_ALIAS_RE():
    return re.compile(r"@\(|\$\(|!\(|\$\[|!\[")


class Aliases(cabc.MutableMapping):
    """Represents a location to hold and look up aliases."""

    def __init__(self, *args, **kwargs):
        self._raw = {}
        self.update(*args, **kwargs)

    def get(self, key, default=None):
        """Returns the (possibly modified) value. If the key is not present,
        then `default` is returned.
        If the value is callable, it is returned without modification. If it
        is an iterable of strings it will be evaluated recursively to expand
        other aliases, resulting in a new list or a "partially applied"
        callable.
        """
        val = self._raw.get(key)
        if val is None:
            return default
        elif isinstance(val, cabc.Iterable) or callable(val):
            return self.eval_alias(val, seen_tokens={key})
        else:
            msg = "alias of {!r} has an inappropriate type: {!r}"
            raise TypeError(msg.format(key, val))

    def eval_alias(self, value, seen_tokens=frozenset(), acc_args=()):
        """
        "Evaluates" the alias ``value``, by recursively looking up the leftmost
        token and "expanding" if it's also an alias.

        A value like ``["cmd", "arg"]`` might transform like this:
        ``> ["cmd", "arg"] -> ["ls", "-al", "arg"] -> callable()``
        where ``cmd=ls -al`` and ``ls`` is an alias with its value being a
        callable.  The resulting callable will be "partially applied" with
        ``["-al", "arg"]``.
        """
        # Beware of mutability: default values for keyword args are evaluated
        # only once.
        if callable(value):
            return partial_eval_alias(value, acc_args=acc_args)
        else:
            expand_path = builtins.__xonsh__.expand_path
            token, *rest = map(expand_path, value)
            if token in seen_tokens or token not in self._raw:
                # ^ Making sure things like `egrep=egrep --color=auto` works,
                # and that `l` evals to `ls --color=auto -CF` if `l=ls -CF`
                # and `ls=ls --color=auto`
                rtn = [token]
                rtn.extend(rest)
                rtn.extend(acc_args)
                return rtn
            else:
                seen_tokens = seen_tokens | {token}
                acc_args = rest + list(acc_args)
                return self.eval_alias(self._raw[token], seen_tokens, acc_args)

    def expand_alias(self, line):
        """Expands any aliases present in line if alias does not point to a
        builtin function and if alias is only a single command.
        """
        word = line.split(" ", 1)[0]
        if word in builtins.aliases and isinstance(self.get(word), cabc.Sequence):
            word_idx = line.find(word)
            expansion = " ".join(self.get(word))
            line = line[:word_idx] + expansion + line[word_idx + len(word) :]
        return line

    #
    # Mutable mapping interface
    #

    def __getitem__(self, key):
        return self._raw[key]

    def __setitem__(self, key, val):
        if isinstance(val, str):
            f = "<exec-alias:" + key + ">"
            if SUB_EXEC_ALIAS_RE.search(val) is not None:
                # We have a sub-command, e.g. $(cmd), to evaluate
                self._raw[key] = ExecAlias(val, filename=f)
            elif isexpression(val):
                # expansion substitution
                lexer = builtins.__xonsh__.execer.parser.lexer
                self._raw[key] = list(map(strip_simple_quotes, lexer.split(val)))
            else:
                # need to exec alias
                self._raw[key] = ExecAlias(val, filename=f)
        else:
            self._raw[key] = val

    def __delitem__(self, key):
        del self._raw[key]

    def update(self, *args, **kwargs):
        for key, val in dict(*args, **kwargs).items():
            self[key] = val

    def __iter__(self):
        yield from self._raw

    def __len__(self):
        return len(self._raw)

    def __str__(self):
        return str(self._raw)

    def __repr__(self):
        return "{0}.{1}({2})".format(
            self.__class__.__module__, self.__class__.__name__, self._raw
        )

    def _repr_pretty_(self, p, cycle):
        name = "{0}.{1}".format(self.__class__.__module__, self.__class__.__name__)
        with p.group(0, name + "(", ")"):
            if cycle:
                p.text("...")
            elif len(self):
                p.break_()
                p.pretty(dict(self))


class ExecAlias:
    """Provides a callable alias for xonsh source code."""

    def __init__(self, src, filename="<exec-alias>"):
        """
        Parameters
        ----------
        src : str
            Source code that will be
        """
        self.src = src if src.endswith("\n") else src + "\n"
        self.filename = filename

    def __call__(
        self, args, stdin=None, stdout=None, stderr=None, spec=None, stack=None
    ):
        execer = builtins.__xonsh__.execer
        frame = stack[0][0]  # execute as though we are at the call site
        execer.exec(
            self.src, glbs=frame.f_globals, locs=frame.f_locals, filename=self.filename
        )

    def __repr__(self):
        return "ExecAlias({0!r}, filename={1!r})".format(self.src, self.filename)


class PartialEvalAliasBase:
    """Partially evaluated alias."""

    def __init__(self, f, acc_args=()):
        """
        Parameters
        ----------
        f : callable
            A function to dispatch to.
        acc_args : sequence of strings, optional
            Additional arguments to prepent to the argument list passed in
            when the alias is called.
        """
        self.f = f
        self.acc_args = acc_args
        self.__name__ = getattr(f, "__name__", self.__class__.__name__)

    def __call__(
        self, args, stdin=None, stdout=None, stderr=None, spec=None, stack=None
    ):
        args = list(self.acc_args) + args
        return self.f(args, stdin, stdout, stderr, spec, stack)

    def __repr__(self):
        return "{name}({f!r}, acc_args={acc_args!r})".format(
            name=self.__class__.__name__, f=self.f, acc_args=self.acc_args
        )


class PartialEvalAlias0(PartialEvalAliasBase):
    def __call__(
        self, args, stdin=None, stdout=None, stderr=None, spec=None, stack=None
    ):
        args = list(self.acc_args) + args
        if args:
            msg = "callable alias {f!r} takes no arguments, but {args!f} provided. "
            msg += "Of these {acc_args!r} were partially applied."
            raise XonshError(msg.format(f=self.f, args=args, acc_args=self.acc_args))
        return self.f()


class PartialEvalAlias1(PartialEvalAliasBase):
    def __call__(
        self, args, stdin=None, stdout=None, stderr=None, spec=None, stack=None
    ):
        args = list(self.acc_args) + args
        return self.f(args)


class PartialEvalAlias2(PartialEvalAliasBase):
    def __call__(
        self, args, stdin=None, stdout=None, stderr=None, spec=None, stack=None
    ):
        args = list(self.acc_args) + args
        return self.f(args, stdin)


class PartialEvalAlias3(PartialEvalAliasBase):
    def __call__(
        self, args, stdin=None, stdout=None, stderr=None, spec=None, stack=None
    ):
        args = list(self.acc_args) + args
        return self.f(args, stdin, stdout)


class PartialEvalAlias4(PartialEvalAliasBase):
    def __call__(
        self, args, stdin=None, stdout=None, stderr=None, spec=None, stack=None
    ):
        args = list(self.acc_args) + args
        return self.f(args, stdin, stdout, stderr)


class PartialEvalAlias5(PartialEvalAliasBase):
    def __call__(
        self, args, stdin=None, stdout=None, stderr=None, spec=None, stack=None
    ):
        args = list(self.acc_args) + args
        return self.f(args, stdin, stdout, stderr, spec)


class PartialEvalAlias6(PartialEvalAliasBase):
    def __call__(
        self, args, stdin=None, stdout=None, stderr=None, spec=None, stack=None
    ):
        args = list(self.acc_args) + args
        return self.f(args, stdin, stdout, stderr, spec, stack)


PARTIAL_EVAL_ALIASES = (
    PartialEvalAlias0,
    PartialEvalAlias1,
    PartialEvalAlias2,
    PartialEvalAlias3,
    PartialEvalAlias4,
    PartialEvalAlias5,
    PartialEvalAlias6,
)


def partial_eval_alias(f, acc_args=()):
    """Dispatches the appropriate eval alias based on the number of args to the original callable alias
    and how many arguments to apply.
    """
    # no partial needed if no extra args
    if not acc_args:
        return f
    # need to dispatch
    numargs = 0
    for name, param in inspect.signature(f).parameters.items():
        if (
            param.kind == param.POSITIONAL_ONLY
            or param.kind == param.POSITIONAL_OR_KEYWORD
        ):
            numargs += 1
        elif name in ALIAS_KWARG_NAMES and param.kind == param.KEYWORD_ONLY:
            numargs += 1
    if numargs < 7:
        return PARTIAL_EVAL_ALIASES[numargs](f, acc_args=acc_args)
    else:
        e = "Expected proxy with 6 or fewer arguments for {}, not {}"
        raise XonshError(e.format(", ".join(ALIAS_KWARG_NAMES), numargs))


#
# Actual aliases below
#


def xonsh_exit(args, stdin=None):
    """Sends signal to exit shell."""
    if not clean_jobs():
        # Do not exit if jobs not cleaned up
        return None, None
    builtins.__xonsh__.exit = True
    print()  # gimme a newline
    return None, None


def xonsh_reset(args, stdin=None):
    """ Clears __xonsh__.ctx"""
    builtins.__xonsh__.ctx.clear()


@lazyobject
def _SOURCE_FOREIGN_PARSER():
    desc = "Sources a file written in a foreign shell language."
    parser = argparse.ArgumentParser("source-foreign", description=desc)
    parser.add_argument("shell", help="Name or path to the foreign shell")
    parser.add_argument(
        "files_or_code",
        nargs="+",
        help="file paths to source or code in the target " "language.",
    )
    parser.add_argument(
        "-i",
        "--interactive",
        type=to_bool,
        default=True,
        help="whether the sourced shell should be interactive",
        dest="interactive",
    )
    parser.add_argument(
        "-l",
        "--login",
        type=to_bool,
        default=False,
        help="whether the sourced shell should be login",
        dest="login",
    )
    parser.add_argument(
        "--envcmd", default=None, dest="envcmd", help="command to print environment"
    )
    parser.add_argument(
        "--aliascmd", default=None, dest="aliascmd", help="command to print aliases"
    )
    parser.add_argument(
        "--extra-args",
        default=(),
        dest="extra_args",
        type=(lambda s: tuple(s.split())),
        help="extra arguments needed to run the shell",
    )
    parser.add_argument(
        "-s",
        "--safe",
        type=to_bool,
        default=True,
        help="whether the source shell should be run safely, "
        "and not raise any errors, even if they occur.",
        dest="safe",
    )
    parser.add_argument(
        "-p",
        "--prevcmd",
        default=None,
        dest="prevcmd",
        help="command(s) to run before any other commands, "
        "replaces traditional source.",
    )
    parser.add_argument(
        "--postcmd",
        default="",
        dest="postcmd",
        help="command(s) to run after all other commands",
    )
    parser.add_argument(
        "--funcscmd",
        default=None,
        dest="funcscmd",
        help="code to find locations of all native functions " "in the shell language.",
    )
    parser.add_argument(
        "--sourcer",
        default=None,
        dest="sourcer",
        help="the source command in the target shell " "language, default: source.",
    )
    parser.add_argument(
        "--use-tmpfile",
        type=to_bool,
        default=False,
        help="whether the commands for source shell should be "
        "written to a temporary file.",
        dest="use_tmpfile",
    )
    parser.add_argument(
        "--seterrprevcmd",
        default=None,
        dest="seterrprevcmd",
        help="command(s) to set exit-on-error before any" "other commands.",
    )
    parser.add_argument(
        "--seterrpostcmd",
        default=None,
        dest="seterrpostcmd",
        help="command(s) to set exit-on-error after all" "other commands.",
    )
    parser.add_argument(
        "--overwrite-aliases",
        default=False,
        action="store_true",
        dest="overwrite_aliases",
        help="flag for whether or not sourced aliases should "
        "replace the current xonsh aliases.",
    )
    parser.add_argument(
        "--suppress-skip-message",
        default=None,
        action="store_true",
        dest="suppress_skip_message",
        help="flag for whether or not skip messages should be suppressed.",
    )
    parser.add_argument(
        "--show",
        default=False,
        action="store_true",
        dest="show",
        help="Will show the script output.",
    )
    parser.add_argument(
        "-d",
        "--dry-run",
        default=False,
        action="store_true",
        dest="dryrun",
        help="Will not actually source the file.",
    )
    return parser


def source_foreign(args, stdin=None, stdout=None, stderr=None):
    """Sources a file written in a foreign shell language."""
    env = builtins.__xonsh__.env
    ns = _SOURCE_FOREIGN_PARSER.parse_args(args)
    ns.suppress_skip_message = (
        env.get("FOREIGN_ALIASES_SUPPRESS_SKIP_MESSAGE")
        if ns.suppress_skip_message is None
        else ns.suppress_skip_message
    )
    if ns.prevcmd is not None:
        pass  # don't change prevcmd if given explicitly
    elif os.path.isfile(ns.files_or_code[0]):
        # we have filename to source
        ns.prevcmd = '{} "{}"'.format(ns.sourcer, '" "'.join(ns.files_or_code))
    elif ns.prevcmd is None:
        ns.prevcmd = " ".join(ns.files_or_code)  # code to run, no files
    foreign_shell_data.cache_clear()  # make sure that we don't get prev src
    fsenv, fsaliases = foreign_shell_data(
        shell=ns.shell,
        login=ns.login,
        interactive=ns.interactive,
        envcmd=ns.envcmd,
        aliascmd=ns.aliascmd,
        extra_args=ns.extra_args,
        safe=ns.safe,
        prevcmd=ns.prevcmd,
        postcmd=ns.postcmd,
        funcscmd=ns.funcscmd,
        sourcer=ns.sourcer,
        use_tmpfile=ns.use_tmpfile,
        seterrprevcmd=ns.seterrprevcmd,
        seterrpostcmd=ns.seterrpostcmd,
        show=ns.show,
        dryrun=ns.dryrun,
    )
    if fsenv is None:
        if ns.dryrun:
            return
        else:
            msg = "xonsh: error: Source failed: {0!r}\n".format(ns.prevcmd)
            msg += "xonsh: error: Possible reasons: File not found or syntax error\n"
            return (None, msg, 1)
    # apply results
    denv = env.detype()
    for k, v in fsenv.items():
        if k in denv and v == denv[k]:
            continue  # no change from original
        env[k] = v
    # Remove any env-vars that were unset by the script.
    for k in denv:
        if k not in fsenv:
            env.pop(k, None)
    # Update aliases
    baliases = builtins.aliases
    for k, v in fsaliases.items():
        if k in baliases and v == baliases[k]:
            continue  # no change from original
        elif ns.overwrite_aliases or k not in baliases:
            baliases[k] = v
        elif ns.suppress_skip_message:
            pass
        else:
            msg = (
                "Skipping application of {0!r} alias from {1!r} "
                "since it shares a name with an existing xonsh alias. "
                'Use "--overwrite-alias" option to apply it anyway.'
                'You may prevent this message with "--suppress-skip-message" or '
                '"$FOREIGN_ALIASES_SUPPRESS_SKIP_MESSAGE = True".'
            )
            print(msg.format(k, ns.shell), file=stderr)


def source_alias(args, stdin=None):
    """Executes the contents of the provided files in the current context.
    If sourced file isn't found in cwd, search for file along $PATH to source
    instead.
    """
    env = builtins.__xonsh__.env
    encoding = env.get("XONSH_ENCODING")
    errors = env.get("XONSH_ENCODING_ERRORS")
    for i, fname in enumerate(args):
        fpath = fname
        if not os.path.isfile(fpath):
            fpath = locate_binary(fname)
            if fpath is None:
                if env.get("XONSH_DEBUG"):
                    print("source: {}: No such file".format(fname), file=sys.stderr)
                if i == 0:
                    raise RuntimeError(
                        "must source at least one file, " + fname + "does not exist."
                    )
                break
        _, fext = os.path.splitext(fpath)
        if fext and fext != ".xsh" and fext != ".py":
            raise RuntimeError(
                "attempting to source non-xonsh file! If you are "
                "trying to source a file in another language, "
                "then please use the appropriate source command. "
                "For example, source-bash script.sh"
            )
        with open(fpath, "r", encoding=encoding, errors=errors) as fp:
            src = fp.read()
        if not src.endswith("\n"):
            src += "\n"
        ctx = builtins.__xonsh__.ctx
        updates = {"__file__": fpath, "__name__": os.path.abspath(fpath)}
        with env.swap(**make_args_env(args[i + 1 :])), swap_values(ctx, updates):
            try:
                builtins.execx(src, "exec", ctx, filename=fpath)
            except Exception:
                print_color(
                    "{RED}You may be attempting to source non-xonsh file! "
                    "{NO_COLOR}If you are trying to source a file in "
                    "another language, then please use the appropriate "
                    "source command. For example, {GREEN}source-bash "
                    "script.sh{NO_COLOR}",
                    file=sys.stderr,
                )
                raise


def source_cmd(args, stdin=None):
    """Simple cmd.exe-specific wrapper around source-foreign."""
    args = list(args)
    fpath = locate_binary(args[0])
    args[0] = fpath if fpath else args[0]
    if not os.path.isfile(args[0]):
        return (None, "xonsh: error: File not found: {}\n".format(args[0]), 1)
    prevcmd = "call "
    prevcmd += " ".join([argvquote(arg, force=True) for arg in args])
    prevcmd = escape_windows_cmd_string(prevcmd)
    args.append("--prevcmd={}".format(prevcmd))
    args.insert(0, "cmd")
    args.append("--interactive=0")
    args.append("--sourcer=call")
    args.append("--envcmd=set")
    args.append("--seterrpostcmd=if errorlevel 1 exit 1")
    args.append("--use-tmpfile=1")
    with builtins.__xonsh__.env.swap(PROMPT="$P$G"):
        return source_foreign(args, stdin=stdin)


def xexec(args, stdin=None):
    """exec [-h|--help] command [args...]

    exec (also aliased as xexec) uses the os.execvpe() function to
    replace the xonsh process with the specified program. This provides
    the functionality of the bash 'exec' builtin::

        >>> exec bash -l -i
        bash $

    The '-h' and '--help' options print this message and exit.

    Notes
    -----
    This command **is not** the same as the Python builtin function
    exec(). That function is for running Python code. This command,
    which shares the same name as the sh-lang statement, is for launching
    a command directly in the same process. In the event of a name conflict,
    please use the xexec command directly or dive into subprocess mode
    explicitly with ![exec command]. For more details, please see
    http://xon.sh/faq.html#exec.
    """
    if len(args) == 0:
        return (None, "xonsh: exec: no args specified\n", 1)
    elif args[0] == "-h" or args[0] == "--help":
        return inspect.getdoc(xexec)
    else:
        denv = builtins.__xonsh__.env.detype()
        try:
            os.execvpe(args[0], args, denv)
        except FileNotFoundError as e:
            return (
                None,
                "xonsh: exec: file not found: {}: {}" "\n".format(e.args[1], args[0]),
                1,
            )


class AWitchAWitch(argparse.Action):
    SUPPRESS = "==SUPPRESS=="

    def __init__(
        self, option_strings, version=None, dest=SUPPRESS, default=SUPPRESS, **kwargs
    ):
        super().__init__(
            option_strings=option_strings, dest=dest, default=default, nargs=0, **kwargs
        )

    def __call__(self, parser, namespace, values, option_string=None):
        import webbrowser

        webbrowser.open("https://github.com/xonsh/xonsh/commit/f49b400")
        parser.exit()


def xonfig(args, stdin=None):
    """Runs the xonsh configuration utility."""
    from xonsh.xonfig import xonfig_main  # lazy import

    return xonfig_main(args)


@unthreadable
def trace(args, stdin=None, stdout=None, stderr=None, spec=None):
    """Runs the xonsh tracer utility."""
    from xonsh.tracer import tracermain  # lazy import

    try:
        return tracermain(args, stdin=stdin, stdout=stdout, stderr=stderr, spec=spec)
    except SystemExit:
        pass


def showcmd(args, stdin=None):
    """usage: showcmd [-h|--help|cmd args]

    Displays the command and arguments as a list of strings that xonsh would
    run in subprocess mode. This is useful for determining how xonsh evaluates
    your commands and arguments prior to running these commands.

    optional arguments:
      -h, --help            show this help message and exit

    example:
      >>> showcmd echo $USER can't hear "the sea"
      ['echo', 'I', "can't", 'hear', 'the sea']
    """
    if len(args) == 0 or (len(args) == 1 and args[0] in {"-h", "--help"}):
        print(showcmd.__doc__.rstrip().replace("\n    ", "\n"))
    else:
        sys.displayhook(args)


def detect_xpip_alias():
    """
    Determines the correct invocation to get xonsh's pip
    """
    if not getattr(sys, "executable", None):
        return lambda args, stdin=None: (
            "",
            "Sorry, unable to run pip on your system (missing sys.executable)",
            1,
        )

    basecmd = [sys.executable, "-m", "pip"]
    try:
        if ON_WINDOWS:
            # XXX: Does windows have an installation mode that requires UAC?
            return basecmd
        elif not os.access(os.path.dirname(sys.executable), os.W_OK):
            return ["sudo"] + basecmd
        else:
            return basecmd
    except Exception:
        # Something freaky happened, return something that'll probably work
        return basecmd


def make_default_aliases():
    """Creates a new default aliases dictionary."""
    default_aliases = {
        "cd": cd,
        "pushd": pushd,
        "popd": popd,
        "dirs": dirs,
        "jobs": jobs,
        "fg": fg,
        "bg": bg,
        "EOF": xonsh_exit,
        "exit": xonsh_exit,
        "quit": xonsh_exit,
        "exec": xexec,
        "xexec": xexec,
        "source": source_alias,
        "source-zsh": ["source-foreign", "zsh", "--sourcer=source"],
        "source-bash": ["source-foreign", "bash", "--sourcer=source"],
        "source-cmd": source_cmd,
        "source-foreign": source_foreign,
        "history": xhm.history_main,
        "replay": replay_main,
        "trace": trace,
        "timeit": timeit_alias,
        "xonfig": xonfig,
        "scp-resume": ["rsync", "--partial", "-h", "--progress", "--rsh=ssh"],
        "showcmd": showcmd,
        "ipynb": ["jupyter", "notebook", "--no-browser"],
        "which": xxw.which,
        "xontrib": xontribs_main,
        "completer": xca.completer_alias,
        "xpip": detect_xpip_alias(),
        "xonsh-reset": xonsh_reset,
    }
    if ON_WINDOWS:
        # Borrow builtin commands from cmd.exe.
        windows_cmd_aliases = {
            "cls",
            "copy",
            "del",
            "dir",
            "echo",
            "erase",
            "md",
            "mkdir",
            "mklink",
            "move",
            "rd",
            "ren",
            "rename",
            "rmdir",
            "time",
            "type",
            "vol",
        }
        for alias in windows_cmd_aliases:
            default_aliases[alias] = ["cmd", "/c", alias]
        default_aliases["call"] = ["source-cmd"]
        default_aliases["source-bat"] = ["source-cmd"]
        default_aliases["clear"] = "cls"
        if ON_ANACONDA:
            # Add aliases specific to the Anaconda python distribution.
            default_aliases["activate"] = ["source-cmd", "activate.bat"]
            default_aliases["deactivate"] = ["source-cmd", "deactivate.bat"]
        if not locate_binary("sudo"):
            import xonsh.winutils as winutils

            def sudo(args):
                if len(args) < 1:
                    print(
                        "You need to provide an executable to run as " "Administrator."
                    )
                    return
                cmd = args[0]
                if locate_binary(cmd):
                    return winutils.sudo(cmd, args[1:])
                elif cmd.lower() in windows_cmd_aliases:
                    args = ["/D", "/C", "CD", _get_cwd(), "&&"] + args
                    return winutils.sudo("cmd", args)
                else:
                    msg = 'Cannot find the path for executable "{0}".'
                    print(msg.format(cmd))

            default_aliases["sudo"] = sudo
    elif ON_DARWIN:
        default_aliases["ls"] = ["ls", "-G"]
    elif ON_FREEBSD or ON_DRAGONFLY:
        default_aliases["grep"] = ["grep", "--color=auto"]
        default_aliases["egrep"] = ["egrep", "--color=auto"]
        default_aliases["fgrep"] = ["fgrep", "--color=auto"]
        default_aliases["ls"] = ["ls", "-G"]
    elif ON_NETBSD:
        default_aliases["grep"] = ["grep", "--color=auto"]
        default_aliases["egrep"] = ["egrep", "--color=auto"]
        default_aliases["fgrep"] = ["fgrep", "--color=auto"]
    else:
        default_aliases["grep"] = ["grep", "--color=auto"]
        default_aliases["egrep"] = ["egrep", "--color=auto"]
        default_aliases["fgrep"] = ["fgrep", "--color=auto"]
        default_aliases["ls"] = ["ls", "--color=auto", "-v"]
    return default_aliases